Flexible Package With Stress Riser Opening

ABSTRACT

The present application provides improved sealed packages and improved methods for making sealed packages. The sealed package includes a first side and a second side, wherein the first side and the second side each comprise a laminate material including an product-side layer and a film layer, the product-side layers of the first and second sides at least partially heat sealed together to form a heat seal between the first and second sides such that the heat seal comprises a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/018,050 filed on Dec. 31, 2007.

FIELD OF THE INVENTION

The present application relates to flexible food packages and more particularly relates to openings for flexible food packages that vent during food preparation.

BACKGROUND

Generally described, packages for both storing and preparing food desirably seal the food during storage and a vent during preparation. For example, packages used to store and then cook vegetables in microwave ovens may need to vent to release steam. Unfortunately, these packages may vent in an unpredictable location and manner, which may interfere with the cooking process.

What is desired, therefore, is a package that can automatically vent steam during cooking from a predictable location. The package may seal the food during storage, and may provide easy access to the food after cooking.

SUMMARY OF THE INVENTION

The present application provides a sealed package. In one exemplary embodiment, the package includes a first side and a second side, wherein the first side and the second side each comprise a laminate material including an product-side layer and a film layer, the product-side layers of the first and second sides at least partially heat sealed together to form a heat seal between the first and second sides such that the heat seal comprises a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material.

The present invention also provides a method for making a sealed package. In an exemplary embodiment, the method includes: (a) providing a laminate material including an product-side layer and a film layer; and (b) heat sealing the product-side layer of a first portion of the laminate material and the product-side layer of a second portion of the laminate material to form a heat seal comprising a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material.

The present invention also provides a method for preparing food. In an exemplary embodiment, the method includes: (a) providing a sealed package comprising a first side and a second side, wherein the first side and the second side each comprise a laminate material including an product-side layer and a film layer, the product-side layers of the first and second sides at least partially heat sealed together to form a heat seal between the first and second sides such that the heat seal comprises a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material, and wherein the sealed package further comprises a food on the inside of the sealed package; and (b) microwaving the sealed package to heat the food and generate steam; wherein the pressure of the steam forms a break in the product-side layer at the location of the stress riser, and wherein the pressure of the steam delaminates the product-side layer and the film layer at the location of the break.

The present invention also provides a heat sealing die for heat sealing a package. In an exemplary embodiment, the heat sealing die includes a first heat seal jaw having a first primary seal face with a first periphery and a first stress-riser seal face extending outwardly away from the first periphery; and a second heat seal jaw having a second primary seal face with a second periphery and a second stress-riser seal face extending outwardly away from the second periphery. The heat sealing die is adapted to compress the first heat seal jaw and the second heat seal jaw about the package to produce a primary heat seal where the first primary seal face and the second primary seal face contact the package and a stress riser adjacent to the primary heat seal where the first stress-riser seal face and the second stress-riser seal face contact the package.

The present invention also provides a system for producing a heat-sealed package. In an exemplary embodiment, the system includes a heat sealing die with a first and a second heat seal jaw and a feeder adapted to feed the package between the first and second heat seal jaws. The first heat seal jaw includes a first primary seal face with a first periphery and a first stress-riser seal face extending outwardly away from the first periphery. The second heat seal jaw includes a second primary seal face with a second periphery and a second stress-riser seal face extending outwardly away from the second periphery. The heat sealing die is adapted to compress the first heat seal jaw and the second heat seal jaw about the package to produce a primary heat seal where the first primary seal face and the second primary seal face contact the package and a stress riser adjacent to the primary heat seal where the first stress-riser seal face and the second stress-riser seal face contact the package.

These and other features of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an end view of a laminate material suitable for use in a sealed package in accordance with an embodiment of this invention.

FIG. 2 shows a side elevation view of a sealed package made in accordance with an embodiment of this invention.

FIG. 3A shows a partial side elevation view of the embodiment illustrated in FIG. 2 featuring a stress riser.

FIG. 3B shows the progression of tearing of the product-side layer and the delamination of the product-side layer and film layer when a steam vent is formed.

FIG. 4 shows an end view of the embodiment illustrated in FIG. 2 featuring a heat seal.

FIG. 5 shows an end view of the embodiment illustrated in FIG. 2 featuring a heat seal vent.

FIG. 6 also shows an end view of the embodiment illustrated in FIG. 2 featuring a heat seal vent.

FIG. 7 shows a perspective view of heat seal dies in accordance with an embodiment of this invention.

FIG. 8 shows a part of a system for producing a heat sealed package having a stress riser.

DETAILED DESCRIPTION

Reference now will be made in detail to various aspects of this invention, including the presently preferred embodiments. Each example is provided by way of explanation of embodiments of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations within the scope of the appended claims and their equivalents.

Methods have been developed according to aspects of this invention for making a sealed package by providing a laminate material and forming a heat seal between the laminate material. Unlike conventional heat seals, which may vent in an unpredictable manner and location, the instant heat seals include a stress riser so that they may reliably vent from a predictable location. Furthermore, because the heat seal is stronger than the bond between the layers of the laminate, the package may vent steam between the layers of the laminate material.

As used herein, the terms “comprise,” “comprising,” “include,” and “including” are intended to be open, non-limiting terms, unless the contrary is expressly indicated.

The Sealed Package

The present application provides improved sealed packages and methods for making sealed packages. According to a particular embodiment, the present application provides sealed packages suitable for preparing food in a microwave oven.

The packages and methods described herein may be useful for packaging essentially any product. The materials and methods especially may be useful for packaging products that are prepared by steaming. Advantageously, the packaging materials may comprise a heat seal between two portions of a laminate material, wherein the heat seal is stronger that the bond between the layers of the laminate material. The package described herein also may include a stress riser in the heat seal. As a result of the stress riser, the laminate packaging material may automatically vent in a predictable manner and location.

Referring now to the drawings, in which like numerals indicate like elements throughout separate views, FIG. 1 shows one embodiment of a suitable laminate material 100. The laminate material 100 may include a film layer 102 and an product-side layer 104.

The film layer 102 may comprise essentially any type of flexible web. Non-limiting examples of suitable film layers include olefin polymer films and biopolymer films. In one embodiment, the film layer 102 comprises an olefin polymer such polypropylene, polyethylene, polyethylene terephthalate, or combinations thereof. In another embodiment, the film layer 102 comprises a biopolymer such as cellulose or polylactic acid. The film layer 102 may comprise an oriented film, and in particular embodiments may comprise a biaxially oriented film. Furthermore, the film layer 102 may comprise multiple layers, such as, for example, a multiple layer coextruded film. In a particular embodiment, the film layer 102 has a thickness 106 in the range from about 0.25 millimeters to about 3 millimeters. More desirably, the film layer 102 has a thickness 106 in the range from about 0.5 millimeters to about 1 millimeters, and, even more desirably, about 0.75 millimeters.

The product-side layer 104 may comprise essentially any type of flexible web suitable for forming a heat seal. Non-limiting examples of suitable product-side layers include polyurethane film and polyethylene film. In a particular embodiment, the product-side layer 104 has a thickness 108 in the range from about 0.5 millimeters to about 3 millimeters. More desirably, the product-side layer 104 has a thickness 108 in the range from about 1 millimeters to about 2.5 millimeters, and, even more desirably, about 0.75 millimeters. It has been discovered that the thickness 108 of the product-side layer 104 may be adjusted to control when the venting occurs. Specifically, if the thickness 108 is increased, then the venting may occur at a later time, and if the thickness 108 is decreased, then the venting may occur at an earlier time.

Referring again to the drawings, FIG. 2 shows one embodiment of a sealed package 110. The sealed package 110 may comprise a first side 112 and a second side 114, each comprising the laminate material 100. The sealed package 110 also may include first and second heat seals 116 and 118 at respective ends 120 and 122 of the sealed package 110. The heat seals 116 and 118 may be formed by heat sealing the product-side layers 104 of the first and second sides 112 and 114 together.

The first and second sides 112 and 114 and the heat seals 116 and 118 form the boundaries of an interior space (not shown) for holding a package material such as food. The first and second sides 112 and 114 are arranged such that the product-side layers 104 face inwardly toward the interior space of the sealed package 110 and the film layers 102 face outwardly.

In a particular embodiment, the heat seals 116 and 118 have a width 123 in the range from about 0.1 centimeters to about 2 centimeters, and preferably about 0.5 centimeters. It has been discovered that the width 123 of heat seal 116 may be adjusted to control when the venting occurs. Specifically, if the width 123 is increased, then the venting may occur at a later time, and if the width 123 is decreased, then the venting may occur at an earlier time. In some embodiments, the width 123 of heat seal 116 is narrower than the width of heat seal 118 as well as any other heat seal on the sealed package 110.

In one embodiment, at least one of the heat seals 116 and 118 may have an interior boundary 124 facing the interior space of the sealed package 110. According to a certain embodiment, the interior boundary 124 of the top heat seal 116 may include a first portion 126 and a second portion 128, referred to here as a stress riser, that extends beyond the first portion 126 toward the interior of the sealed package 110 (as shown in FIG. 3A). In a certain embodiment, the first portion 126 of the heat seal interior boundary 124 is substantially linear. The stress riser 128 may have essentially any shape. Non-limited examples of suitable shapes include a “V” shape, a “U” shape, or a square shape.

As illustrated in FIG. 3A, the stress riser 128 may have a length 132 and a width 134. It has been discovered that the length 132 of the stress riser 128 may be adjusted to control when the venting occurs. Specifically, if the length 132 is increased, then the venting may occur at an earlier time, and if the length 132 is decreased, then the venting may occur at a later time. In a particular embodiment, the stress riser 128 has a length 132 in the range from about 0.1 centimeters to about 2 centimeters. More desirably, the stress riser 128 has a length 132 in the range from about 0.25 millimeters to about 1 centimeters, and, even more desirably, about 0.5 centimeters. It also has been discovered that the width 134 of the stress riser 128 may be adjusted to control when the venting occurs. Specifically, if the width 134 is increased, then the venting may occur at a later time, and if the width 134 is decreased, then the venting may occur at an earlier time. In a particular embodiment, the stress riser 128 has a width 134 in the range from about 0.1 centimeters to about 2 centimeters. More desirably, the stress riser 128 has a width 134 in the range from about 0.25 millimeters to about 1 centimeters, and, even more desirably, about 0.5 centimeters. In a preferred embodiment, the stress riser 128 comprises a “V” shape. It has been discovered that the angle between the “V” may be adjusted to control when the venting occurs. Specifically, if the angle is increased, then the venting may occur at a later time, and if the angle is decreased, then the venting may occur at an earlier time.

Importantly, the stress riser 128 may cause the package 110 to form a break in a predictable location. As pressure in the package 200 builds, the force of the pressure on the laminate material 100 may be greatest in the area of the stress riser 128. As a result, the laminate material 100 may break at the location of the s stress riser 128. Because the vent may predictably form at the stress riser 128, the package 110 may be constructed so that the venting always occurs near the top of the package, which may prevent the package 110 from leaking moisture into a microwave.

FIG. 3B illustrates the progression of tearing of the product-side layer 104 and the delamination of the film layer 102 from the product-side layer 104 when a steam vent is formed. When steam is produced in the package, the product-side layer 104 initially tears at the stress focal point 170. The tear quickly continues along the interior boundary 124 first along the edges of the stress riser 128 and then continuing along a portion of the interior boundary 124 of the heat seal 116 as shown by the arrows originating at the stress focal point 170. As the product-side layer 104 tears, steam intrudes between the product-side layer 104 and the film layer 102 causing the two layers to delaminate. The concentric arcs in FIG. 3B illustrate the progression of the delamination as the steam peels the layers apart across the top of heat seal 116. Once the steam crosses the width of the heat seal 116, the steam vents out of the package.

FIG. 4 shows an end view of one embodiment of the top heat seal 116. The heat seal 116 may be between the product-side layer 104 of a portion of the first side 112 of the laminate material 100 and the product-side layer 104 of a portion of the second side 112 of the laminate material 100.

Importantly, heat seal 116 between the product-side layers 104 may be stronger than the bond between the product-side layer 104 and the film layer 102. As a result, the package 110 may vent steam in a very predictable manner. As described above, the stress riser 128 may cause the laminate material 100 to form a break at the location of the stress riser 128. Because the heat seal 116 between the product-side layers 104 may be stronger than the bond between the product-side layer 104 and the film layer 102, the break may not extend through both the product-side layer 104 and the film layer 102 of the laminate material 100, and the package 110 may not vent steam through a path between the product-side layers 104. Rather, the break only may extend through the product-side layer 104, and the steam may vent through a path that extends through the break in the product-side layer 104 and then between the product-side layer 104 and the film layer 102.

FIGS. 5 and 6 show an end view of one embodiment venting through the heat seal 116. The stress riser 128 may cause a break (not shown) through the product-side layer 104 through which the steam may travel. The steam may then travel through a vent 140 between the film layer 102 and the product-side layer 104. Venting in this manner may provide significant advantages over venting through either (1) a break that extends directly through both the product-side layer 104 and the film layer 102 of the laminate material 100 or (2) a path between the product-side layers 104. Because the venting may occur through the relatively longer path between the layers of the laminate material 100, the package may maintain steam pressure and avoid a complete loss of steam that could detrimentally interfere with the food preparation process. Further, the heat and moisture in the steam may cause the film layer 102 and the product-side layer 104 to gradually delaminate during the food preparation. This delamination may create a larger vent 142. The larger vent 142 may allow a greater quantity of steam to escape during the later stages of the food preparation. In some embodiments, the bond between the product-side layer 104 and film layer 102 is heat and moisture sensitive. In these embodiments, the heat and moisture of the steam acts to loosen the bond between the product-side layer 104 and film layer 102 to improve the delamination.

The package 110 may further comprise additional heat seals. For example, the package 110 may include a side seals and/or a back seal.

Making the Sealed Package

Also embodied in this invention are methods of making a package. In one embodiment, the method comprises the steps of (a) providing a laminate material including an product-side layer and a film layer; and (b) heat sealing the product-side layer of a first portion of the laminate material and the product-side layer of a second portion of the laminate material to form a heat seal comprising a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material.

The heat seal may be formed using essentially any method known in the art. In one embodiment, the forming step comprises contacting the first portion of the laminate and the second portion of the laminate and applying heat. The forming step may form a stress riser of essentially any shape. Non-limited examples of suitable shapes include a “V” shape, a “U” shape, or a square shape.

In a preferred embodiment, the forming step comprises pressing the first portion and second portion together between two heated jaws comprising stress rising faces. FIG. 7 shows a perspective view of one embodiment of heat seal jaws 150 and 152. The heat seal jaw 150 may include grooves 154, and the heat seal jaw 152 may include lands 156. The grooves 154 may be adapted to receive the lands 156 so as to create a heat seal. The heat seal jaw 150 may further include a stress riser face 158, and the heat seal jaw 152 may further include a stress riser face 160. The stress riser faces 158 and 160 may create a stress riser. The stress riser faces 158 and 160 may have essentially any shape. Non-limited examples of suitable shapes include a “V” shape, a “U” shape, or a square shape. The heat seal jaws 150 and 152 may also include a blade slot 172 for receiving a cutting blade.

FIG. 8 illustrates a part of a system for producing a heat sealed package. A feeder feeds the package material 174 through a heat-sealing die between the heat seal jaw 150 and the heat seal jaw 152 (not shown here) along a direction of travel as indicated by the arrow. Once the package material 174 has traveled a predesignated distance, the heat seal jaws 150 and 152 compress around the package material 174 and form a heat seal. A cutting blade then passes through slot 172 to cut the package material 174 within heat-sealed region. In an exemplary embodiment, the package material 174 may be filled with product before passing between the heat seal jaws 152.

As can be seen most clearly in FIG. 8, the heat seal jaws 150 and 152 have primary heat seal faces 176 for forming the primary heat seal on the package. The heat seal jaws 150 and 152 also include stress-riser seal faces 178 which are adjacent to and extend outwardly away from the periphery 180 of the primary heat seal faces 176. The reader will appreciate that such an arrangement will produce the heat seal 116 having the stress riser 128 of FIG. 3A.

Preparing Food with the Package

Also embodied in this invention are methods of preparing food. In one embodiment, the method comprises (a) providing a sealed package comprising a first side and a second side, wherein the first side and the second side each comprise a laminate material including an product-side layer and a film layer, the product-side layers of the first and second sides at least partially heat sealed together to form a heat seal between the first and second sides such that the heat seal comprises a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material, and wherein the sealed package further comprises a food on the inside of the sealed package; and (b) microwaving the sealed package to heat the food and generate steam, wherein the pressure of the steam forms a break in the product-side layer at the location of the stress riser, wherein the pressure of the steam delaminates the product-side layer and the film layer at the location of the break.

It should be understood that the foregoing relates only to the preferred embodiments of the present application and that numerous changes and modifications may be made herein without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof. 

1. A sealed package, comprising: a first side and a second side, wherein the first side and the second side each comprise a laminate material including a product-side layer and a film layer, the product-side layers of the first and second sides at least partially heat sealed together to form a heat seal between the first and second sides such that the heat seal comprises a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material.
 2. The sealed package of claim 1, wherein the film layer comprises at least one olefin polymer.
 3. The sealed package of claim 2, wherein the olefin polymer comprises polypropylene or polyethylene terephthalate.
 4. The sealed package of claim 1, wherein the film layer comprises a biopolymer.
 5. The sealed package of claim 4, wherein the biopolymer comprises cellulose.
 6. The sealed package of claim 1, wherein the product-side layer comprises polyurethane.
 7. The sealed package of claim 1, wherein the product-side layer comprises polyethylene.
 8. The sealed package of claim 1, wherein the package has an interior space, the heat seal includes an interior boundary facing the interior space, the interior boundary having a first portion, and the stress riser includes a second portion of the interior boundary extending beyond the first portion of the interior boundary toward the interior space or away from the interior space.
 9. The sealed package of claim 8, wherein the stress riser comprises a “V” shape.
 10. The sealed package of claim 8, wherein the stress riser comprises a “U” shape.
 11. The sealed package of claim 1, wherein the sealed package furthers comprises a food on the inside of the sealed package.
 12. The sealed package of claim 11, wherein the food comprises a vegetable.
 13. The sealed package of claim 1, wherein the product-side layer is adapted to rupture at the stress riser and vent steam out of the sealed package between the product-side layer and the film layer.
 14. A method of making a sealed package, comprising the steps of: (a) providing a laminate material including an product-side layer and a film layer; and (b) heat sealing the product-side layer of a first portion of the laminate material and the product-side layer of a second portion of the laminate material to form a heat seal comprising a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material.
 15. The method of claim 14, wherein the heat sealing step forms a heat seal including an interior boundary facing an interior space of the sealed package, the interior boundary having a first portion, and the stress riser includes a second portion of the interior boundary extending beyond the first portion of the interior boundary toward the interior space or away from the interior space.
 16. The method of claim 15, wherein the heat sealing step comprises forming a stress riser with a “V” shape.
 17. The method of claim 15, wherein the heat sealing step comprises forming a stress riser with a “U” shape.
 18. The method of claim 14, wherein the heat sealing step comprises pressing the first portion and second portion together between two heated dies comprising stress rising faces.
 19. A method of preparing food, comprising: (a) providing a sealed package comprising a first side and a second side, wherein the first side and the second side each comprise a laminate material including an product-side layer and a film layer, the product-side layers of the first and second sides at least partially heat sealed together to form a heat seal between the first and second sides such that the heat seal comprises a stress riser, wherein the heat seal is stronger than the bond between the product-side layer and the film layer of the laminate material, and wherein the sealed package further comprises a food on the inside of the sealed package; and (b) microwaving the sealed package to heat the food and generate steam; wherein the pressure of the steam forms a break in the product-side layer at the location of the stress riser, and wherein the pressure of the steam delaminates the product-side layer and the film layer at the location of the break.
 20. A heat sealing die for heat sealing a package comprising: (a) a first heat seal jaw having a first primary seal face with a first periphery and a first stress-riser seal face extending outwardly away from the first periphery; and (b) a second heat seal jaw having a second primary seal face with a second periphery and a second stress-riser seal face extending outwardly away from the second periphery; wherein the heat sealing die is adapted to compress said first heat seal jaw and said second heat seal jaw about the package to produce a primary heat seal where the first primary seal face and the second primary seal face contact the package and a stress riser adjacent to the primary heat seal where the first stress-riser seal face and the second stress-riser seal face contact the package.
 21. A system for producing a heat-sealed package comprising: (a) a heat sealing die comprising (i) a first heat seal jaw having a first primary seal face with a first periphery and a first stress-riser seal face extending outwardly away from the first periphery; and (ii) a second heat seal jaw having a second primary seal face with a second periphery and a second stress-riser seal face extending outwardly away from the second periphery; wherein the heat sealing die is adapted to compress said first heat seal jaw and said second heat seal jaw about the package to produce a primary heat seal where the first primary seal face and the second primary seal face contact the package and a stress riser adjacent to the primary heat seal where the first stress-riser seal face and the second stress-riser seal face contact the package; and (b) a feeder adapted to feed the package between the first heat seal jaw and the second heat seal jaw. 